Delphi 7 for Beginners: Learn the Basics of Visual Programming and Object-Oriented Design
Delphi 7 Tutorial.epub: A Comprehensive Guide for Beginners
If you are looking for a powerful and easy-to-learn programming language that can help you create desktop, web, and mobile applications for various platforms, then you might want to consider Delphi 7. In this article, you will learn what Delphi 7 is, why you should learn it, and how you can get started with it.
Delphi 7 Tutorial.epub
Getting Started with Delphi 7
Delphi 7 is an integrated development environment (IDE) that allows you to write, compile, debug, and run applications written in Object Pascal, a modern version of the Pascal language. Delphi 7 was released in 2002 by Borland, and it is still widely used by many developers today.
To install Delphi 7 on your computer, you need to have a copy of the installation CD or download the setup file from the internet. You can find various versions of Delphi 7 online, such as the Personal Edition, the Professional Edition, or the Enterprise Edition. Each version has different features and limitations, so you need to choose the one that suits your needs best.
Once you have installed Delphi 7 on your computer, you can launch the IDE by clicking on the Start menu, then Programs, then Borland Delphi 7, then Delphi 7. The IDE consists of several windows that help you create and manage your projects. Some of the main windows are:
The Menu Bar: This contains various menus that allow you to access different commands and options.
The Tool Bar: This contains icons that provide shortcuts to some of the most common commands.
The Object Inspector: This shows the properties and events of the selected component or form.
The Form Designer: This allows you to design the user interface of your application by dragging and dropping components from the Component Palette.
The Component Palette: This contains a list of components that you can use in your application, such as buttons, labels, edit boxes, and more.
The Code Editor: This allows you to write and edit the source code of your application.
The Project Manager: This shows the files and folders that belong to your project.
The Debugger: This allows you to test and debug your application by setting breakpoints, watching variables, stepping through code, and more.
To create a new project in Delphi 7, you can click on the File menu, then New, then Application. This will create a blank form and a unit file for you. A form is a window that displays the user interface of your application, and a unit is a file that contains the source code of your application. You can save your project by clicking on the File menu, then Save All. You can name your project as you like, but the default names are Project1.dpr for the project file, Unit1.pas for the unit file, and Form1.dfm for the form file.
To write the source code of your application, you can switch to the Code Editor by clicking on the View menu, then Code. The Code Editor has two tabs: one for the interface section and one for the implementation section. The interface section declares the types, variables, constants, and procedures that are visible to other units in your project. The implementation section defines the actual code of your procedures and functions. You can use various keywords, symbols, and operators to write your code in Object Pascal. You can also use comments to explain or document your code. Comments are ignored by the compiler and can be either single-line or multi-line.
To compile and run your application, you can click on the Run menu, then Run. This will build your project and execute it. You can also use the F9 key as a shortcut. If there are any errors or warnings in your code, they will be displayed in the Message window at the bottom of the IDE. You can fix them and try again until your application runs successfully.
Basic Concepts of Delphi Programming
In this section, you will learn some of the basic concepts of Delphi programming that you need to know before you start creating more complex applications. These include:
Variables: These are named containers that store values of different data types, such as integers, strings, booleans, and more. You can declare variables using the var keyword, followed by the name and type of the variable. For example: var x: Integer;
Data Types: These are categories of values that determine how a variable can store and manipulate data. Delphi supports various data types, such as ordinal, real, string, boolean, pointer, array, record, set, file, class, interface, and variant. Each data type has a range of possible values and a size in memory. For example: Integer is an ordinal data type that can store whole numbers from -2147483648 to 2147483647 and occupies 4 bytes in memory.
Operators: These are symbols that perform arithmetic, logical, relational, bitwise, or assignment operations on one or more operands. Operands are values or variables that are involved in an operation. For example: x + y is an expression that uses the addition operator (+) to add two operands (x and y).
Expressions: These are combinations of operands and operators that produce a value when evaluated. Expressions can be simple or complex, depending on the number and type of operands and operators involved. For example: x * (y + z) is a complex expression that uses parentheses to change the order of evaluation.
Statements: These are instructions that tell the compiler what to do with expressions or variables. Statements can be simple or compound, depending on the number and type of expressions or variables involved. For example: x := x + 1; is a simple statement that uses the assignment operator (:=) to assign the value of x + 1 to x.
Comments: These are texts that are ignored by the compiler and are used to explain or document your code. Comments can be single-line or multi-line, depending on how you start and end them. For example: // This is a single-line comment or This is a multi-line comment
Here is an example of how you can use these concepts to write a simple program that calculates and displays the area of a circle:
// Declare variables var radius: Real area: Real; pi: Real; begin // Assign a value to pi pi := 3.14; // Prompt the user to enter the radius WriteLn('Enter the radius of the circle: '); // Read the radius from the user input ReadLn(radius); // Calculate the area using the formula area := pi * radius * radius; // Display the result WriteLn('The area of the circle is ', area); end.
This program will output something like this:
Enter the radius of the circle: 10 The area of the circle is 314
Object-Oriented Programming with Delphi
One of the main features of Delphi is that it supports object-oriented programming (OOP). OOP is a programming paradigm that organizes data and behavior into reusable units called objects. Objects are instances of classes, which are templates that define the properties and methods of a group of similar objects. OOP allows you to create modular, maintainable, and reusable code that can model real-world entities and scenarios.
To create a class in Delphi, you can use the type keyword, followed by the name and definition of the class. For example:
type TPerson = class // Declare private fields private FName: String; FAge: Integer; // Declare public properties and methods public // Constructor constructor Create(Name: String; Age: Integer); // Destructor destructor Destroy; override; // Property to get or set name property Name: String read FName write FName; // Property to get or set age property Age: Integer read FAge write FAge; // Method to display person's details procedure ShowDetails; end;
This code defines a class called TPerson, which represents a person with a name and an age. The class has two private fields, FName and FAge, which store the values of the name and age properties. The class also has a constructor, which is a special method that creates and initializes an object of the class, and a destructor, which is a special method that destroys and frees an object of the class. The class also has two public properties, Name and Age, which allow access to the private fields, and a public method, ShowDetails, which displays the person's details on the screen.
To create an object of a class in Delphi, you can use the new operator, followed by the name of the class and any parameters for the constructor. For example:
var person1: TPerson; begin // Create an object of TPerson class with name 'Alice' and age 25 person1 := TPerson.Create('Alice', 25);
This code declares a variable called person1 of type TPerson, and assigns it a new object of TPerson class with name 'Alice' and age 25. The constructor of TPerson class is called with these parameters to initialize the object.
To access or modify the properties or methods of an object in Delphi, you can use the dot operator (.), followed by the name of the property or method. For example:
begin // Display person1's details person1.ShowDetails; // Change person1's name to 'Bob' person1.Name := 'Bob'; end;
This code calls the ShowDetails method of person1 object to display its details on the screen, and then assigns a new value to its Name property.
To destroy an object of a class in Delphi, you can use the free method, which calls the destructor of the class and releases the memory allocated for the object. For example:
begin // Destroy person1 object person1.Free; end;
This code calls the free method of person1 object, which invokes its destructor and frees its memory.
Working with Forms and Controls
One of the most common types of applications that you can create with Delphi is a graphical user interface (GUI) application. A GUI application consists of one or more forms that display various controls that allow the user to interact with the application. A form is a window that contains the user interface of the application, and a control is a component that performs a specific function, such as displaying text, accepting input, or executing commands.
To create a GUI application in Delphi, you can use the Form Designer to design the layout and appearance of your forms and controls. You can drag and drop controls from the Component Palette to the Form Designer, and adjust their properties and events using the Object Inspector. You can also write code for your forms and controls using the Code Editor.
Some of the most common controls that you can use in your GUI applications are:
TButton: This is a control that executes a command when clicked by the user.
TLabel: This is a control that displays a text on the form.
TEdit: This is a control that allows the user to enter and edit a single line of text.
TListBox: This is a control that displays a list of items that the user can select from.
TComboBox: This is a control that combines an edit box and a list box, allowing the user to enter or select an item from a drop-down list.
TCheckBox: This is a control that allows the user to select or deselect an option by clicking on a check box.
TRadioButton: This is a control that allows the user to select one option from a group of mutually exclusive options by clicking on a radio button.
Here is an example of how you can create a simple GUI application that converts Celsius to Fahrenheit using Delphi:
Create a new project by clicking on File, then New, then Application.
Save your project by clicking on File, then Save All. Name your project as TempConverter.dpr, your unit as Unit1.pas, and your form as Form1.dfm.
Drag and drop a TLabel, an TEdit, and a TButton from the Component Palette to the Form Designer. Arrange them as shown in the figure below.
Select the TLabel and change its Caption property to 'Celsius:' using the Object Inspector.
Select the TEdit and change its Name property to 'edtCelsius' using the Object Inspector.
Select the TButton and change its Caption property to 'Convert' and its Name property to 'btnConvert' using the Object Inspector.
Double-click on the btnConvert control to create an event handler for its OnClick event. This will switch to the Code Editor and generate an empty procedure for you.
Write the following code inside the procedure:
var celsius: Real; fahrenheit: Real; begin // Read celsius value from edtCelsius control celsius := StrToFloat(edtCelsius.Text); // Convert celsius to fahrenheit using formula fahrenheit := (celsius * 9/5) + 32; // Display fahrenheit value using message box ShowMessage('Fahrenheit: ' + FloatToStr(fahrenheit)); end;
This code declares two variables, celsius and fahrenheit, of type Real, which can store decimal numbers. It then reads the value entered by the user in the edtCelsius control and converts it to a Real value using the StrToFloat function. It then applies the formula for converting Celsius to Fahrenheit and stores the result in the fahrenheit variable. Finally, it displays the fahrenheit value using a message box with the ShowMessage function.
Save your project and run it by clicking on Run, then Run. You should see something like this:
Enter a value in Celsius and click on Convert. You should see something like this: